The present invention relates to a nebulizer, or an ultrasonic wave mist generator and in particular, relates to such an apparatus which has a piezoelectric vibrator at the bottom of a water container for converting liquid water to mist.
In an ultrasonic nebulizer, the water surface is violently vibrated with ultrasonic wave frequency by a piezoelectric vibrator which is mounted at the bottom of the water, and water at the water surface is converted to mist. In order to obtain high performance of conversion, the energy by the vibrator must be concentrated on a small active area of the water surface. The water vibration at the peripheral region of the water surface would interfere with the vibration at the active area, and would decrease the conversion efficiency.
Conventionally, JP patent publication 36386/1980 has been known for improving efficiency for atomization. That publication describes a plate or a gate which is located between a piezoelectric vibrator and the water surface, and said plate has a first large aperture for passing the main lobe of vibration, and a plurality of second small peripheral apertures for passing side lobes of vibration. It is theorized that the second apertures function such that side lobes of vibration are diffracted, and are cancelled by each other, and so do not disturb the main lobe vibration. Therefore, the conversion efficiency from water to mist is improved.
However, the efficiency of atomization by said plate is only 5-7%.
Another prior art reference is JP patent laid open publication 23738/1985, in which a porous member is mounted in a water container except the center portion just above a vibrator. The porous member absorbs the undesired side lobe vibration at the periphery of the water surface.
However, it has the disadvantages that the efficiency improvement is still small, and the presence of a porous member causes some trouble in cleaning the water container.